This invention relates to a solid-state laser device for use in emitting an output laser beam by pumping a solid-state laser medium by a semiconductor laser unit.
In a conventional solid-state laser device of the type described, a solid-state laser medium, such as Nd:YAG, is arranged in a laser resonator and pumped by an excitation laser beam to generate an oscillation laser beam. The oscillation laser beam is emitted through the laser resonator as an output laser beam. Specifically, the solid-state laser medium has an optical axis, a pair of end surfaces transverse to the optical axis, and a side surface contiguous to the end surfaces along the optical axis. The solid-state laser medium may be pumped by the excitation laser beam from either at least one of the end surfaces or the side surface of the solid-state laser medium. The excitation laser beam is usually generated by a laser diode.
In addition, it often happens that a wavelength conversion element, such as KTP, is located inside or outside of the laser resonator so as to emit the output laser beam which has a wavelength different from that of the oscillation laser beam. This structure enables oscillation of a blue or a green laser beam. Herein, an optical element, such as a wavelength conversion element, will be generally called an optical function element.
In the meantime, it is a recent trend that such a solid-state laser device is applicable to a wide variety of equipments and that strict limitations are very often imposed on a laser characteristic, such as intensity of the output laser beam, and any other optical characteristics related to a longitudinal mode, a transverse mode, and beam pointing. At any time, the output laser beam should be strictly stabilized in the solid-state laser device.
However, it has been found out that the conventional solid-state laser device can not completely satisfy all of the above-mentioned optical characteristics. This is because the solid-state laser medium and the laser resonator can not be completely regulated or controlled about a temperature in the conventional solid-state laser device.
For example, disclosure is made by Barer et al in U.S. Pat. No. 4,653,056 about an Nd-YAG laser which comprises a laser diode, an Nd:YAG laser rod, a frequency doubler, such as a KTP, and a laser resonator, all of which are housed in a housing and which will be referred to as optical components hereinunder. In addition, a Peltier cooler is also arranged in the housing and is connected to a temperature control circuit to control a temperature of the laser diode. However, it is to be noted here that only the temperature of the laser diode is controlled by the Peltier cooler and the temperature control circuit, independently of the other optical components. This makes temperature control of a whole of the Nd:YAG laser insufficient or incomplete.